1. Technical Field
This disclosure relates to semiconductor fabrication and more particularly, to a method for improving recessed conductive barrier interfaces after chemical mechanical polishing.
2. Description of the Related Art
In stacked capacitor structures, a barrier layer is typically employed between a conductive plug, which connects to an access transistor and an electrode of the capacitor. The barrier layer may include TaSiN, which is typically used as a barrier for oxygen and metal diffusion. In stacked capacitor designs, which employ high dielectric constant materials, TaSiN is used as an oxygen and platinum diffusion barrier. For other device structures, TaSiN may used as a barrier for such materials like copper interconnects.
Where TaSiN is used as a recessed barrier, first the composite film (TaSiN) is deposited and then to achieve the recessed barrier, it undergoes a chemical mechanical polish (CMP) operation. The CMP operation oxidizes the surface and therefore causes contact resistance problems. These contact resistance problems include non-linear behavior in the electrical performance of the capacitor device and high contact resistance in the order of 100 kilo-Ohms or more.
Therefore, a need exists for a method for removing an oxidized layer from a top of a barrier layer, and in particular, a recessed barrier layer after chemical mechanical polishing.
A method for cleaning an oxidized diffusion barrier layer, in accordance with the present invention, includes providing a conductive diffusion barrier layer employed for preventing oxygen and metal diffusion therethrough and providing a wet chemical etchant including hydrofluoric acid. The diffusion barrier layer is etched with the wet chemical etchant to remove oxides from the diffusion barrier layer such that by employing the wet chemical etchant linear electrical behavior is achieved through the diffusion barrier layer.
A method for cleaning an oxidized diffusion barrier layer after chemical mechanical polishing, in accordance with the present invention, includes forming a conductive diffusion barrier layer, employed for preventing oxygen and metal diffusion therethrough, on a surface of an etch mask and in a recess formed in the etch mask, and polishing the conductive diffusion barrier layer to remove the conductive diffusion barrier layer from the surface of the etch mask such that the diffusion barrier layer remains in the recess. A wet chemical etchant including hydrofluoric acid is provided, and the diffusion barrier layer is etched in the recess with the wet chemical etchant to remove oxides from the diffusion barrier layer such that by employing the wet chemical etchant linear electrical behavior is achieved through the diffusion barrier layer.
A method for cleaning an oxidized diffusion barrier layer employed in a stacked capacitor structure, in accordance with the present invention, includes forming a conductive plug through a dielectric layer for contacting an access transistor, recessing the conductive plug below a surface of the dielectric layer, forming a conductive diffusion barrier layer, employed for preventing oxygen and metal diffusion therethrough, on a surface of an etch mask and in a recess formed in the etch mask, the etch mask formed on the dielectric layer, polishing the conductive diffusion barrier layer to remove the conductive diffusion barrier layer from the surface of the etch mask such that the diffusion barrier layer remains in the recess, providing a wet chemical etchant including hydrofluoric acid, etching the diffusion barrier layer in the recess with the wet chemical etchant to remove oxides from the diffusion barrier layer such that by employing the wet chemical etchant linear electrical behavior is achieved through the diffusion barrier layer and patterning an electrode in contact with the diffusion barrier layer in the recess.
In other methods, the barrier layer may preferably include tantalum. Suitable materials for the barrier layer may include TaSiN, TaAlN, TiAlN and TiSiN. The wet chemical etchant may include diluted hydrofluoric acid, or a buffered hydrofluoric acid. The diluted hydrofluoric acid may include a dilution ratio of parts water to parts hydrofluoric acid of between about 10:1 to about 200:1. The step of polishing the conductive barrier layer may include the step of polishing by chemical mechanical polishing employing a slurry. The slurry may include an oxidizing agent, which oxidizes the conductive barrier layer. The electrode preferably includes platinum.
These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings.